What is Defibrillation? Why is Defibrillation Important?
Every year, over 350,000 people die from Sudden Cardiac Arrest (SCA) in the United States, making it a leading cause of death in the country. That’s the equivalent of 1 death every 90 seconds.
Sudden Cardiac Arrest primarily occurs when the heart suddenly starts beating in an irregular rhythm, typically ventricular fibrillation or pulseless ventricular tachycardia.
The purpose of the heart is to deliver oxygen throughout the body with strong, regular beats. When Sudden Cardiac Arrest happens, the heart begins twitching uncontrollably rather than beating regularly. Consequently, the heart becomes incapable of delivering oxygen to the brain. Without oxygen, severe brain damage occurs and victims of cardiac arrest will die within minutes.
Fortunately, there is a treatment for the irregular heart rhythms or arrhythmias that cause Sudden Cardiac Arrest. An electrical defibrillation shock, often delivered by an Automated External Defibrillator (AED), restarts the heart during SCA and restores a regular heartbeat.
If a person collapses suddenly and is not responsive, they should be treated with both cardiopulmonary resuscitation (CPR) and defibrillation shocks from an AED. CPR acts as an artificial pump by manually pushing on the heart and circulating blood to the brain, but it’s not as efficient as an actual heartbeat. CPR also doesn’t actually restart the heart, an AED is needed for that.
Defibrillation is the only therapy to treat someone in cardiac arrest. Every minute that a person in Sudden Cardiac Arrest does not receive defibrillation, their chances of survival drop by 7-10%, making rapid defibrillation imperative for survival and one of the key steps in saving a life from Sudden Cardiac Arrest.
How Does Defibrillation Work?
In a normal, healthy heart, electrical impulses trigger a coordinated sequence of muscle contractions that enable the heart to pump blood. When the heart is in ventricular fibrillation or ventricular tachycardia, the electrical signals that control the heart are scrambled. Therefore, the heart muscle is not contracting in an organized fashion. A defibrillation shock from an AED resets these scrambled signals and enables the heart to beat normally.
A “shock” of electrical current from a defibrillator depolarizes most of the heart and ends the arrhythmia. After this depolarization, there is typically a brief period where the electrical signals in the heart pause before a normal heartbeat is reestablished.
This is what happens when a patient suffers cardiac arrest and is resuscitated with an AED:
- The patient’s heart goes from normal sinus rhythm to ventricular fibrillation. The patient will collapse suddenly due to oxygen deprivation.
- While in either ventricular fibrillation or pulseless ventricular tachycardia, the patient is clinically dead without an organized heartbeat but they are not yet biologically dead. Their heart still has electrical activity. The heart is “fibrillating” or quivering, but it’s not enough to sustain life.
- When a patient receives a “shock” from an AED, the energy from the AED passes between the electrode pads and through the patient’s heart.
- The sudden burst of energy through the patient’s heart causes their heart cells to depolarize, stopping the chaotic and ineffective rhythm, otherwise known as defibrillating (de-fibrillating).
- After the heart has been defibrillated, the heart goes back into a normal sinus rhythm wherein it starts recirculating oxygen-rich blood throughout their body. Their skin color may return to normal and, in some cases, they will start breathing on their own.
Now that you know more about defibrillation, check out how AEDs work.
Why is Rapid Defibrillation Important?
In the “chain of survival,” which involves a series of four steps that are needed for successful SCA resuscitation, early defibrillation is the most important link. Since defibrillation is the most effective treatment for VF cardiac arrest, the longer a patient has to wait for a defibrillation shock, the lower the chances of survival.
Although cardiologists say that CPR can prolong the neurological viability of a patient in VF for as long as ten minutes using chest compressions, CPR alone cannot restore a normal rhythm and defibrillation is required to regain heart function.
Automated External Defibrillators Decrease Time-to-Defibrillation
Automated External Defibrillators (AEDs) are small, portable defibrillators designed mainly for out-of-hospital settings.
The device, which was developed in 1973, consists of computer circuitry, batteries, and capacitors that enable it to measure cardiac rhythm and deliver shock therapy to patients in cardiac arrest. AEDs are often placed in public places such as malls, swimming pools, police cruisers, airplanes, and homes for use by both Emergency Medical Services (EMS) personnel and trained laypersons.
Different AEDs have varying levels of capability. These range from pure shock-inducing AEDs, semi-automatic varieties, to fully automated systems that diagnose the heart rhythm and deliver the shock automatically if needed.
Commonly, the time-to-defibrillation is dependent on how quickly EMS personnel can get to the scene of an emergency and use their advanced equipment. With an AED, however, first responders such as firefighters and police officers, or even minimally trained bystanders and family members, can rapidly administer defibrillation and thus improve the prognosis of the patient.
Aside from their simplicity, AEDs are designed with safety in mind, so that even errors in an application do not result in harm to the patient or person administering the shock.
Increasing the number of AEDs that are publically available has been one of the recommendations/requirements that many health authorities in the industrialized world have instituted. In the United States, over 200,000 AEDs are sold every year. In many of the areas where AEDs have been made available, there has been a significant reduction in the time-to-defibrillation and, thus, an improvement in SCA survival rates. A study of casinos where security personnel and on-ground medical personnel had AEDs found that the meantime to defibrillation was 2.9 minutes whereas paramedics take an average of 9.8 minutes to arrive.
Time-to-Defibrillation and SCA Survival Rates
Faster response times are associated with a greater likelihood of SCA survival, making AEDs critical in remote or congested places where EMS response times are slower. Various studies have found a correlation between survival rates from SCA and the use of AEDs.
Medical experts recommend that defibrillation be attempted as quickly as possible after the onset of cardiac arrest because survival from VF is determined primarily by the time-to-defibrillation.
The survival rate from SCA decreases between 7 and 10 percent for every minute that the patient has to wait for defibrillation.
“Relation of collapse to CPR and defibrillation to survival: simplified model. Graphical representation of simplified (includes collapse to CPR and collapse to defibrillation only) predictive model of survival after witnessed, out-of-hospital cardiac arrest due to VF. Each curve represents change in probability of survival as delay (minutes) to defibrillation increases for a given collapse-to-CPR interval (minutes).”
A study involving 13,769 out-of-hospital cardiac arrests found that survival rates to hospital discharge were 7% with no form of resuscitation attempt, 9% when only CPR was performed and 38% when AED shock therapy was given.
Another study of 105 patients whose initial rhythm was VF, the survival rate was 74% for those who received their first defibrillation no later than three minutes after the witnessed collapse and 49% for those who received their first defibrillation three minutes after the witnessed collapse.
In a closely related experimental study conducted in the Piacenza region of Italy, researchers provided 1285 lay volunteers with 39 AEDs. The volunteers, who had no traditional training in CPR responded to all reported cases of SCA alongside regular EMS over a period of 22 months during which important metrics were recorded. The volunteers handled 143 SCA cases, including un-witnessed and non-shockable SCA, registering an average arrival time of 4.8 minutes compared to 6.2 minutes for regular EMS. More importantly, the survival to hospital discharge rate for patients attended to by the volunteers was three times higher than with EMS intervention (10.5% versus 3.3%).
These research statistics, as well as a vast wealth of anecdotal evidence, underline the critical role that AEDs have to play in the management of SCA. They are cost-effective, safe, and research has shown them to improve survival rates in the most critical locations where emergency services take longer to respond.